(1) Field of the Invention
The present invention relates generally to III-nitride semiconductors and more particularly to crucibles for growing III-nitride semiconductor substrates such as aluminum nitride (AlN). Use of the crucible of this invention may enable the growth of relatively large and high quality III-nitride single crystals.
(2) Background Information
Wide bandgap semiconductor devices, based on III-nitride semiconductors, are expected to find application in several opto-electronic technologies in the areas of short wavelength emission and detection. Aluminum nitride and high aluminum concentration alloys of aluminum nitride with gallium nitride and/or with indium nitride are potentially important III-nitride semiconductors for producing deep-UV light emitting diodes with potential applications including solid-state white lighting, sterilization and disinfectant devices, compact analytical devices for the biotechnology and pharmaceutical markets, bioagent detection systems, compact uv light sources for covert communication by the Department of Defense, and for short wavelength lasers for high density data storage. In addition, single-crystal substrates of aluminum nitride are attractive for the fabrication of III-nitride semiconductor, high power radio frequency, millimeter wave, and microwave devices needed for future wireless communication base stations and for Department of Defense applications. However, one of the factors limiting the maturation of aluminum nitride, and other III-nitride, technology has been the absence of high-quality bulk nitride substrates.
One promising method for the growth of aluminum nitride single crystals for such substrates is the sublimation-recondensation technique first developed by Slack and McNelly (xe2x80x9cGrowth of High Purity AlN Crystalsxe2x80x9d, J. Cryst. Growth 34, 263 (1976) and xe2x80x9cAlN Single Crystalsxe2x80x9d, J. Cryst. Growth 42, 560 (1977)), both of which are fully incorporated by reference herein. However, one of the drawbacks that limited the maximum size of the crystals was the development of leaks in the tungsten crucibles, which ultimately lead to the failure thereof, through which aluminum gas may escape. The development of crucibles that substantially eliminates this problem may provide for the growth of relatively large aluminum nitride single crystals.
Therefore there exists a need for an improved crucible for growth of III-nitride semiconductor single crystals and in particular AlN single crystals.
One aspect of the present invention includes a sealable tungsten crucible for growing a III-nitride semiconductor crystal. The crucible includes an elongated wall structure extending in a longitudinal direction. The wall structure defines an interior crystal growth cavity and includes a plurality of tungsten grains. The wall structure has a thickness dimension extending in a direction substantially perpendicular to the longitudinal direction, the thickness dimension being at least about 1.5 times the average tungsten grain size.
In another aspect, this invention includes a sealable tungsten crucible for growing a III-nitride semiconductor crystal. The crucible includes an elongated wall structure extending in a longitudinal direction. The wall structure defines an interior crystal growth cavity and includes a plurality of tungsten grains. The grains effectively form at least first and second layers, the first layer including grains disposed on an inside surface of the crucible and the second layer being adjacent to the first layer.
In still another aspect, this invention includes a method for fabricating a tungsten crucible for use in growing aluminum nitride single crystals. The method includes providing a bar of powder metallurgy tungsten and machining an elongated wall structure extending in a longitudinal direction. The wall structure defines an interior crystal growth cavity and includes a plurality of tungsten grains. The grains effectively form at least first and second layers, the first layer including grains disposed on an inside surface of the crucible and the second layer being adjacent to the first layer.
In yet another aspect, this invention includes a method for fabricating an aluminum nitride single crystal. The method includes providing a tungsten crucible having an elongated wall structure extending in a longitudinal direction; the wall structure defining an interior crystal growth cavity and including a plurality of tungsten grains, which effectively form at least first and second layers, the first layer including grains disposed on an inside surface of the crucible and the second layer being adjacent the first layer. The method further includes charging the crucible with aluminum nitride, sealing the crucible, and heating at least a portion of the crucible to a temperature in excess of about 2000 degrees C.